WELL; Vital Signs | Patterns: Early Marijuana Use Linked to I.Q. Loss

By BENEDICT CAREY

Published: August 28, 2012

marijuana as teenagers and continued to use it heavily for decades lost a few I.Q. points along the way, while those who started in adulthood did not, researchers reported on Monday.

The findings, from a study tracking people's habits from childhood through middle age, suggest that the developing teenage brain is especially vulnerable to drug use, the authors concluded. The research appears in Proceedings of the National Academy of Sciences.">

People in a study who began smoking marijuana as teenagers and continued to use it heavily for decades lost a few I.Q. points along the way, while those who started in adulthood did not, researchers reported on Monday.

The findings, from a study tracking people's habits from childhood through middle age, suggest that the developing teenage brain is especially vulnerable to drug use, the authors concluded. The research appears in Proceedings of the National Academy of Sciences.

The new report draws on periodic interviews with 1,037 people tracked from birth to age 38, who talked about how often they smoked marijuana and whether it was causing any problems.

"Adolescent-onset cannabis users showed significant I.Q. declines, and more persistent use was associated with greater declines," said the lead author, Madeline H. Meier, a postdoctoral researcher at Duke University.

The study participants who used marijuana heavily from high school through age 38 scored 8 points lower on an I.Q. test than they had when originally tested, as 13-year-olds. I.Q. scores are usually very stable, and those who did not use marijuana or started as adults showed no real change, averaging about 100.

"We know that there are developmental changes occurring in the teen years and up through the early 20s, and the brain may be especially vulnerable during this time," Dr. Meier said.

This is a more complete version of the story than the one that appeared in print.

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marijuana as teenagers and continued to use it heavily for decades lost a few I.Q. points along the way, while those who started in adulthood did not, researchers reported on Monday.

The findings, from a study tracking people's habits from childhood through middle age, suggest that the developing teenage brain is especially vulnerable to drug use, the authors concluded. The research appears in Proceedings of the National Academy of Sciences.">